Interview Question: Boring Old Clock

Sample Question #213 (brainteaser)

What’s the first time after 3 o’clock that the hour and minute hands on a clock face overlap each other?

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One Response to Interview Question: Boring Old Clock

  1. Brett says:

    ANSWER
     
    This kind of clock hands question is very popular, and easy to solve.
     
    We know that every hour the hour hand moves 360/12=30 degrees around the clock face. Since there are 60 minutes in an hour, this means the hour hand moves 30/60=0.5 degrees per minute. The minute hand moves 360/60=6 degrees per minute. Therefore, let x be the target time in minutes, for this question we have (since at 3 o’clock the hour hand is at 90 degrees)
     
         90 +  x/2 = 6x  ==> x = 16.36
     
    So the time would be 3:16:22.
     

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